1. Field of the Invention
This invention relates to a control apparatus for hydraulic elevators.
2. Description of Background
In general, hydraulic elevators are controlled by flow control valves.
According to the conventional control method, in the case of rising of an elevator cage, a hydraulic pump is operated at a constant speed, and the speed of the cage is controlled by a flow control valve. Unnecessary discharge of the pump is flowed back to a tank. In the case of descending of the cage, the speed of the cage is controlled by controlling oil flow from a hydraulic cylinder to the tank owing to the cage weight.
In this control method, oil temperature is raised by energy loss, because the oil is circulated in rising operation. During a descending operation, the potential energy of the cage is consumed as pyrexia of oil.
The oil flow through the valve is controlled by a speed controller so as to run the cage with a predetermined speed pattern. If oil temperature and load pressure are constant values, an actual run curve accords with the speed pattern "A" shown in FIG. 14.
In FIG. 14, the cage is started by an activate command, and accelerated to the rated speed V0. The cage is raised to the point of a decelerating switch, and starts deceleration for stopping at a floor. The cage is raised at a constant leveling speed V1, and stopped at the point of a stopping switch. But, oil temperature varies for the above mentioned reason, and load pressure varies in dependence on the actual number of passengers. The variations of oil temperature and load pressure cause variation in the viscosity of the oil. As a result, the run curve does not accord with the speed pattern because the volumetric efficiency of the hydraulic pump is lowered due to variation in the viscosity of the oil.
When the cage is rising, the discharge of the hydraulic pump decreases when the temperature or pressure is a high value. The discharge increases when the temperature or pressure is a low value. The curve "B" of FIG. 14 indicates an actual run curve when the oil temperature or load pressure is a high value. The curve "C" indicates an actual run curve when the oil temperature or load pressure is a low value. When the cage is descending, the opposite phenomena are occurred.
In the case of the run curve "B", the service for passengers become worse because it takes a long time to run between floors. In the case of the run curve "C", the cage does not stop at floors smoothly, and passengers feel uncomfortable. In order to solve these problems, variable speed patterns are prepared so that actual run curves coincide with the pattern "A" without relation to variations of load pressure and oil temperature. Actually, suitable parameters are selected from a parameter table corresponding to input data from an oil temperature sensor and a load pressure sensor.
As it is difficult to model the characteristics of the valve with physical rules, a statical model is used generally. But to make a statical model it is necessary to obtain many homogeneous data. A large amount of manpower and a long time are required to obtain these data. As the concept of the term "homogeneous data" is not definite, if many data are obtained, the data may not indicate the exact characteristics of the hydraulic elevator. Furthermore, the data can not be adaptable to all hydraulic elevator systems for lack of commonality.
Further difficulty in modeling characteristics of the valve with physical rules occurs because the characteristics of hydraulic system are varied for various reasons, for example, oil temperature, load pressure and hydraulic pipe length.
Also, recently fuzzy reasoning theory has been developed and various applications therefore considered. Reference is made to Mamdani et al, "Fuzzy Reasoning and its Applications", Acedemic Press, Inc., 1981, and Dubois et al, "Fuzzy Sets and Systems: Theory and Application", Academic Press Inc., 1980 as background reference materials in the field of fuzzy reasoning.